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Effect of alkali pre-treatment of jute on the formation of jute-based carbon fibers
Materials Letters 65 (2011) 1492–1494
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Effect of alkali pre-treatment of jute on the formation of jute-based carbon fibers Donghwan Cho a,⁎, Jin Myung Kim a, In Seong Song a, Ikpyo Hong b a b
Department of Polymer Science and Engineering, Kumoh National Institute of Technology, Gumi, Gyeongbuk 730–701, Republic of Korea Carbon Materials Research Group, New Materials and Component Research Center, Research Institute of Industrial Science and Technology, Pohang, 790–600, Republic of Korea
a r t i c l e
i n f o
Article history: Received 14 October 2010 Accepted 10 February 2011 Available online 22 February 2011 Keywords: Jute-based carbon fiber Alkali pre-treatment Fiber morphology Characterization
a b s t r a c t In the present study, the effect of alkali pre-treatment of jute on the formation of jute-based carbon fibers was investigated. Jute fibers were pre-treated at various NaOH concentrations and then carbonized at 700 °C. It was noticeable that the morphology of jute-based carbon fiber was distinctly changed in the case of NaOH pre-treatment at 10 wt.%, exhibiting the dense cross-section that the cells in raw jute fiber completely disappeared after carbonization. Also, the weight loss and thermal shrinkage, and ATR–FTIR and Raman spectra were compared between the untreated and pre-treated jute and jute-based carbon fibers. It was concluded that the pre-treatment with 10 wt.% NaOH done to raw jute fibers played a positive role in the formation of jute-based carbon fibers. © 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Recently, biomass-based products easily obtainable from natural resources have attracted attention in academia and industry [1–3]. This is due to their advantages like sustainability, recyclability, costeffectiveness, environmentally friendliness, etc. [4]. If carbon fibers or activated carbon fibers can be prepared from biomass-based natural fibers, which are abundant in nature and less expansive, it would be desirable and useful although the fibers are not discontinuous, limited in fiber length and relatively low in the mechanical property in comparison with conventional rayon-based and PAN-based carbon fibers. Jute fiber (Corchorus capsularis L.) has often been used because it is one of the cheapest cellulose-based natural fibers and has high Young's modulus among many other natural fibers [5]. It also consists of relatively high cellulose and lignin components. Significant weight loss and thermal shrinkage can be occurred during carbonization of natural fibers [6]. The physical, chemical and morphological characteristics of cellulosed-based carbon fibers significantly depend not only on the heat-treatment condition but also on the chemical pre-treatment. Consequently, the objective of the study is to investigate the effect of the NaOH-based chemical pre-treatment of jute on the morphology, weight reduction, thermal shrinkage and ATR–FTIR and Raman spectral changes occurred in jute-based carbon fibers.
Jute fiber bundles (BW-D grade) were supplied from Bangladesh Jute Institute, Bangladesh. The average fiber length of the bundles was 70 to 80 mm. The bundles were dried at 60 °C for 24 h in an oven prior to use. Prior to each carbonization process, jute fiber bundles were chemically pre-treated with sodium hydroxide. The chemical pretreatment of each natural fiber bundle was conducted by soaking the bundle into 5, 10 and 15 wt.% NaOH solutions for 60 min, respectively. After the pre-treatment, natural fibers in the bundle were neutralized to reach pH 6.5 by rinsing them with distilled water and then dried at 80 °C for 24 h in a convection oven. The carbonization of jute fibers was performed individually using a tube-type Siliconit furnace with an inner diameter of 90 mm, a tube length of 1000 mm and a heating zone of 250 mm according to a preprogrammed heat-treatment profile. Jute fiber bundles freely resting on a graphite plate were carbonized at 700 °C with the heating rate of 1 °C/min with purging nitrogen (99.9% purity, 150 ml/min). The jute fibers carbonized at 700 °C without and with chemical pretreatment were characterized by means of analytical methods. Scanning electron microscopy (SEM, Tescan VEGA II LMU, JEOL JSM-6380) was used to observe the cross-section of jute before and after the pretreatment and carbonization. Each fiber was fractured in a liquid nitrogen bath for microscopic observations. All the samples were coated with platinum for 3 min by a sputtering method. Attenuated total reflection–Fourier transform infrared (ATR–FTIR, Vertex 80v, Bruker Biospin) spectroscopy was performed to examine the chemical change occurring on the fiber surfaces after carbonization. The wavenumber accuracy was better than 0.01 cm− 1. The scan rate was 16 cm− 1 per 100 scan/s. Raman spectroscopy (inVia .Raman, Renishaw Plc.) equipped with Nd YAG laser was used to examine the change of G and D bands. The wavelength was 514 nm and the resolution was 4 cm− 1.
⁎ Corresponding author. Tel.: +82 54 478 7688; fax: +82 54 478 7710. E-mail address: [email protected] (D. Cho). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.02.050
D. Cho et al. / Materials Letters 65 (2011) 1492–1494
1493
Table 1 Dimensional shrinkage and weight loss occurred in the untreated and treated jute fibers during carbonization. Chemical pre-treatment
Dimensional shrinkage (%)
Weight loss (%)
No pre-treatment 5 wt.% NaOH-treated 10 wt.% NaOH-treated 15 wt.% NaOH-treated
22.2 18.3 16.9 16.2
82.4 76.4 75.7 71.5
3. Results and discussion Table 1 compares the percent dimensional shrinkage and weight loss of jute fibers without and with NaOH pre-treatment at different concentrations occurred in the furnace during carbonization at 700 °C. Raw jute fibers, which were sufficiently dried before the heattreatment, exhibited the dimensional shrinkage of about 22% and the weight loss of about 82% after the carbonization. Both the dimensional shrinkage and weight loss were reduced in the jute fibers with alkali pre-treatment and with increasing NaOH concentration. This may be explained by that the alkali treatment done to jute fibers can contribute to removing hemicellulose, low molecular weight components and surface impurities existing on the fibers. The removal of such the components may lead to an increase of the thermal stability. The removal of hemicellulose component and the increased thermal stability by alkali treatment of jute fibers have been reported elsewhere [7]. The possible reason for the increased weight loss from 10 wt.% to 15 wt.%, compared to the weight loss result from 5 wt.% to 10 wt.%, is that hemicelluloses and lignin components existing in jute fiber were removed much by 15 wt.% NaOH and it may lead to increased weight reduction during carbonization, resulting in the decreased fiber diameter. Fig. 1 displays the SEM micrographs of the cross-sections of jute fibers before and after carbonization. Raw jute fibers consist of a number of cells, as typically found in cellulose-based natural fibers [2]. After carbonization, it was obvious that the inner structure (struts between the cells) of the fiber became dense, showing the smaller cells with different sizes. It seemed that some cells were fused or combined together indicating that re-organization of the inner structure may be occurred during the carbonization. The SEM images clearly showed the alkali treatment effect on the morphology of jute fibers and jute-based carbon fibers. The crosssection of jute fiber became dense with increasing NaOH concentration
Fig. 2. ATR–FTIR spectra of raw and carbonized jute fibers without and with NaOH pretreatment.
before carbonization. After carbonization, it seemed that the crosssection became denser with increasing NaOH concentration. At 5 wt.%, most of the struts between the cells disappeared through the transverse direction of jute fiber. At 10 wt.% and higher, no inner cells existed in the fiber, indicating that the full densification through the fiber cross-section was occurred. As a result, the fiber diameter was decreased by the alkali treatment as well as by the carbonization, resulting in the dimensional shrinkage and weight loss, as mentioned earlier. The alkali-treatment done to jute fibers removed the surface impurities and hemicellulose. The removal may be effective at higher alkali concentrations. It turns out that the carbonization yield of jute can be somewhat increased by the alkali-treatment. Other minor components remaining in the fiber after the pre-treatment can be removed by thermal decomposition occurring in the fiber during the carbonization. Most of the cellulose structure was lost, accompanying chemical bond breakage and structural changes at the heat-treatment stages. It led to remarkable thermal shrinkage, diameter reduction and weight loss in the fiber, as similarly occurred in the case of carbonizing a rayon-based carbon fiber precursor. Fig. 2 shows the ATR–FTIR spectra of raw jute fibers and carbonized jute fibers without and with chemical pre-treatment at different concentrations. The result indicated that OH, C―O, and C O groups
Fig. 1. SEM micrographs showing the cross-sections of (A) raw, (B) 5 wt.% NaOH, (C) 10 wt.% NaOH, and (D) 15 wt.% NaOH-treated jute fibers. The micrographs (E) to (H) were observed from their cross-sections after carbonization of (A) to (D), respectively.
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D. Cho et al. / Materials Letters 65 (2011) 1492–1494
Fig. 3. Raman spectra of raw and carbonized jute fibers without and with NaOH pre-treatment.
existed on the raw jute fiber surfaces, reflecting the presence of cellulose, hemicelluloses and lignin components therein. After carbonization, the absorption band near 3400 cm− 1 completely disappeared and the peak intensities around 1700 cm− 1 and 1000 cm− 1 were significantly reduced in the absence of pre-treatment and completely disappeared with NaOH pre-treatment. It can be said that the cellulose structure was lost, generating an intermediate structure being converted to a carbonized fiber. The absorption bands revealed that the NaOH treatment played a positive role in forming jute-based carbon fibers. Fig. 3 presents the Raman spectra for the carbonized jute fibers without and with the pre-treatment. It seemed that the variation of Gband at 1580 cm− 1 was greater than that of D-band at 1340 cm− 1. The ID/IG ratio of carbonized jute fibers was lowest with 10 wt.% NaOH. The average value of the ID/IG ratio of jute fibers carbonized without and with the pre-treatment was obtained from five samples and summarized as follows. Untreated: 0.74, 5 wt.% NaOH-treated: 0.76, 10 wt.% NaOH-treated: 0.71, and 15 wt.%-treated: 0.75. The result was noted that jute fibers treated with 10 wt.% NaOH can be carbonized favorably, giving rise to the lowest ID/IG ratio. This turns out that jute fibers carbonized after pre-treating with 10 wt.% NaOH have developed carbon structure, compared to the fibers without pretreatment or with pre-treatment at other NaOH concentrations. 4. Conclusions The present study demonstrated that appropriate pre-treatment of jute fibers with NaOH prior to carbonization at 700 °C can distinctly
modify the fiber morphology along the transverse direction. The cross-section of the jute-based carbon fiber pre-treated with 10 wt.% NaOH became dense, resulting in complete disappearance of the inner cells in the jute fiber. It was concluded that the pre-treatment with 10 wt.% NaOH done to raw jute fibers played a positive role in the formation of jute-based carbon fibers.
Acknowledgment This research has been financially supported by the R & D Program (Project no: 10033111) for Industrial Fundamental Technology of the Korean Ministry of Knowledge Economy.
References [1] Inagaki M, Nishikawa T, Sakuratani K, Katakura T, Konno H, Morozumi E. Carbon 2004;42:890–3. [2] Phan NH, Rio S, Faur C, Coq LL, Cloirec PL, Nguyen TH. Carbon 2006;44:2569–77. [3] Yun CH, Park YH, Park CR. Carbon 2001;39:559–67. [4] Lee HS, Cho D, Han SO. Macromol Res 2008;16:411–7. [5] Rahman S. In: Müssig J, editor. Industrial applications of natural fibres: structure, properties and technical applications. West Sussex: John Wiley & Sons Ltd; 2010. p. 135. [6] Yoon SB, Cho CW, Cho D, Park JK, Lee JY. Carbon Lett 2008;9:308–15. [7] Seo JM, Cho D, Park WH, Han SO, Hwang TW, Choi CH, et al. J Biobased Mater Bioenergy 2007;1:331–40.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Effect of alkali pre-treatment of jute on the formation of jute-based carbon fibers Donghwan Cho a,⁎, Jin Myung Kim a, In Seong Song a, Ikpyo Hong b a b
Department of Polymer Science and Engineering, Kumoh National Institute of Technology, Gumi, Gyeongbuk 730–701, Republic of Korea Carbon Materials Research Group, New Materials and Component Research Center, Research Institute of Industrial Science and Technology, Pohang, 790–600, Republic of Korea
a r t i c l e
i n f o
Article history: Received 14 October 2010 Accepted 10 February 2011 Available online 22 February 2011 Keywords: Jute-based carbon fiber Alkali pre-treatment Fiber morphology Characterization
a b s t r a c t In the present study, the effect of alkali pre-treatment of jute on the formation of jute-based carbon fibers was investigated. Jute fibers were pre-treated at various NaOH concentrations and then carbonized at 700 °C. It was noticeable that the morphology of jute-based carbon fiber was distinctly changed in the case of NaOH pre-treatment at 10 wt.%, exhibiting the dense cross-section that the cells in raw jute fiber completely disappeared after carbonization. Also, the weight loss and thermal shrinkage, and ATR–FTIR and Raman spectra were compared between the untreated and pre-treated jute and jute-based carbon fibers. It was concluded that the pre-treatment with 10 wt.% NaOH done to raw jute fibers played a positive role in the formation of jute-based carbon fibers. © 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Recently, biomass-based products easily obtainable from natural resources have attracted attention in academia and industry [1–3]. This is due to their advantages like sustainability, recyclability, costeffectiveness, environmentally friendliness, etc. [4]. If carbon fibers or activated carbon fibers can be prepared from biomass-based natural fibers, which are abundant in nature and less expansive, it would be desirable and useful although the fibers are not discontinuous, limited in fiber length and relatively low in the mechanical property in comparison with conventional rayon-based and PAN-based carbon fibers. Jute fiber (Corchorus capsularis L.) has often been used because it is one of the cheapest cellulose-based natural fibers and has high Young's modulus among many other natural fibers [5]. It also consists of relatively high cellulose and lignin components. Significant weight loss and thermal shrinkage can be occurred during carbonization of natural fibers [6]. The physical, chemical and morphological characteristics of cellulosed-based carbon fibers significantly depend not only on the heat-treatment condition but also on the chemical pre-treatment. Consequently, the objective of the study is to investigate the effect of the NaOH-based chemical pre-treatment of jute on the morphology, weight reduction, thermal shrinkage and ATR–FTIR and Raman spectral changes occurred in jute-based carbon fibers.
Jute fiber bundles (BW-D grade) were supplied from Bangladesh Jute Institute, Bangladesh. The average fiber length of the bundles was 70 to 80 mm. The bundles were dried at 60 °C for 24 h in an oven prior to use. Prior to each carbonization process, jute fiber bundles were chemically pre-treated with sodium hydroxide. The chemical pretreatment of each natural fiber bundle was conducted by soaking the bundle into 5, 10 and 15 wt.% NaOH solutions for 60 min, respectively. After the pre-treatment, natural fibers in the bundle were neutralized to reach pH 6.5 by rinsing them with distilled water and then dried at 80 °C for 24 h in a convection oven. The carbonization of jute fibers was performed individually using a tube-type Siliconit furnace with an inner diameter of 90 mm, a tube length of 1000 mm and a heating zone of 250 mm according to a preprogrammed heat-treatment profile. Jute fiber bundles freely resting on a graphite plate were carbonized at 700 °C with the heating rate of 1 °C/min with purging nitrogen (99.9% purity, 150 ml/min). The jute fibers carbonized at 700 °C without and with chemical pretreatment were characterized by means of analytical methods. Scanning electron microscopy (SEM, Tescan VEGA II LMU, JEOL JSM-6380) was used to observe the cross-section of jute before and after the pretreatment and carbonization. Each fiber was fractured in a liquid nitrogen bath for microscopic observations. All the samples were coated with platinum for 3 min by a sputtering method. Attenuated total reflection–Fourier transform infrared (ATR–FTIR, Vertex 80v, Bruker Biospin) spectroscopy was performed to examine the chemical change occurring on the fiber surfaces after carbonization. The wavenumber accuracy was better than 0.01 cm− 1. The scan rate was 16 cm− 1 per 100 scan/s. Raman spectroscopy (inVia .Raman, Renishaw Plc.) equipped with Nd YAG laser was used to examine the change of G and D bands. The wavelength was 514 nm and the resolution was 4 cm− 1.
⁎ Corresponding author. Tel.: +82 54 478 7688; fax: +82 54 478 7710. E-mail address: [email protected] (D. Cho). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.02.050
D. Cho et al. / Materials Letters 65 (2011) 1492–1494
1493
Table 1 Dimensional shrinkage and weight loss occurred in the untreated and treated jute fibers during carbonization. Chemical pre-treatment
Dimensional shrinkage (%)
Weight loss (%)
No pre-treatment 5 wt.% NaOH-treated 10 wt.% NaOH-treated 15 wt.% NaOH-treated
22.2 18.3 16.9 16.2
82.4 76.4 75.7 71.5
3. Results and discussion Table 1 compares the percent dimensional shrinkage and weight loss of jute fibers without and with NaOH pre-treatment at different concentrations occurred in the furnace during carbonization at 700 °C. Raw jute fibers, which were sufficiently dried before the heattreatment, exhibited the dimensional shrinkage of about 22% and the weight loss of about 82% after the carbonization. Both the dimensional shrinkage and weight loss were reduced in the jute fibers with alkali pre-treatment and with increasing NaOH concentration. This may be explained by that the alkali treatment done to jute fibers can contribute to removing hemicellulose, low molecular weight components and surface impurities existing on the fibers. The removal of such the components may lead to an increase of the thermal stability. The removal of hemicellulose component and the increased thermal stability by alkali treatment of jute fibers have been reported elsewhere [7]. The possible reason for the increased weight loss from 10 wt.% to 15 wt.%, compared to the weight loss result from 5 wt.% to 10 wt.%, is that hemicelluloses and lignin components existing in jute fiber were removed much by 15 wt.% NaOH and it may lead to increased weight reduction during carbonization, resulting in the decreased fiber diameter. Fig. 1 displays the SEM micrographs of the cross-sections of jute fibers before and after carbonization. Raw jute fibers consist of a number of cells, as typically found in cellulose-based natural fibers [2]. After carbonization, it was obvious that the inner structure (struts between the cells) of the fiber became dense, showing the smaller cells with different sizes. It seemed that some cells were fused or combined together indicating that re-organization of the inner structure may be occurred during the carbonization. The SEM images clearly showed the alkali treatment effect on the morphology of jute fibers and jute-based carbon fibers. The crosssection of jute fiber became dense with increasing NaOH concentration
Fig. 2. ATR–FTIR spectra of raw and carbonized jute fibers without and with NaOH pretreatment.
before carbonization. After carbonization, it seemed that the crosssection became denser with increasing NaOH concentration. At 5 wt.%, most of the struts between the cells disappeared through the transverse direction of jute fiber. At 10 wt.% and higher, no inner cells existed in the fiber, indicating that the full densification through the fiber cross-section was occurred. As a result, the fiber diameter was decreased by the alkali treatment as well as by the carbonization, resulting in the dimensional shrinkage and weight loss, as mentioned earlier. The alkali-treatment done to jute fibers removed the surface impurities and hemicellulose. The removal may be effective at higher alkali concentrations. It turns out that the carbonization yield of jute can be somewhat increased by the alkali-treatment. Other minor components remaining in the fiber after the pre-treatment can be removed by thermal decomposition occurring in the fiber during the carbonization. Most of the cellulose structure was lost, accompanying chemical bond breakage and structural changes at the heat-treatment stages. It led to remarkable thermal shrinkage, diameter reduction and weight loss in the fiber, as similarly occurred in the case of carbonizing a rayon-based carbon fiber precursor. Fig. 2 shows the ATR–FTIR spectra of raw jute fibers and carbonized jute fibers without and with chemical pre-treatment at different concentrations. The result indicated that OH, C―O, and C O groups
Fig. 1. SEM micrographs showing the cross-sections of (A) raw, (B) 5 wt.% NaOH, (C) 10 wt.% NaOH, and (D) 15 wt.% NaOH-treated jute fibers. The micrographs (E) to (H) were observed from their cross-sections after carbonization of (A) to (D), respectively.
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D. Cho et al. / Materials Letters 65 (2011) 1492–1494
Fig. 3. Raman spectra of raw and carbonized jute fibers without and with NaOH pre-treatment.
existed on the raw jute fiber surfaces, reflecting the presence of cellulose, hemicelluloses and lignin components therein. After carbonization, the absorption band near 3400 cm− 1 completely disappeared and the peak intensities around 1700 cm− 1 and 1000 cm− 1 were significantly reduced in the absence of pre-treatment and completely disappeared with NaOH pre-treatment. It can be said that the cellulose structure was lost, generating an intermediate structure being converted to a carbonized fiber. The absorption bands revealed that the NaOH treatment played a positive role in forming jute-based carbon fibers. Fig. 3 presents the Raman spectra for the carbonized jute fibers without and with the pre-treatment. It seemed that the variation of Gband at 1580 cm− 1 was greater than that of D-band at 1340 cm− 1. The ID/IG ratio of carbonized jute fibers was lowest with 10 wt.% NaOH. The average value of the ID/IG ratio of jute fibers carbonized without and with the pre-treatment was obtained from five samples and summarized as follows. Untreated: 0.74, 5 wt.% NaOH-treated: 0.76, 10 wt.% NaOH-treated: 0.71, and 15 wt.%-treated: 0.75. The result was noted that jute fibers treated with 10 wt.% NaOH can be carbonized favorably, giving rise to the lowest ID/IG ratio. This turns out that jute fibers carbonized after pre-treating with 10 wt.% NaOH have developed carbon structure, compared to the fibers without pretreatment or with pre-treatment at other NaOH concentrations. 4. Conclusions The present study demonstrated that appropriate pre-treatment of jute fibers with NaOH prior to carbonization at 700 °C can distinctly
modify the fiber morphology along the transverse direction. The cross-section of the jute-based carbon fiber pre-treated with 10 wt.% NaOH became dense, resulting in complete disappearance of the inner cells in the jute fiber. It was concluded that the pre-treatment with 10 wt.% NaOH done to raw jute fibers played a positive role in the formation of jute-based carbon fibers.
Acknowledgment This research has been financially supported by the R & D Program (Project no: 10033111) for Industrial Fundamental Technology of the Korean Ministry of Knowledge Economy.
References [1] Inagaki M, Nishikawa T, Sakuratani K, Katakura T, Konno H, Morozumi E. Carbon 2004;42:890–3. [2] Phan NH, Rio S, Faur C, Coq LL, Cloirec PL, Nguyen TH. Carbon 2006;44:2569–77. [3] Yun CH, Park YH, Park CR. Carbon 2001;39:559–67. [4] Lee HS, Cho D, Han SO. Macromol Res 2008;16:411–7. [5] Rahman S. In: Müssig J, editor. Industrial applications of natural fibres: structure, properties and technical applications. West Sussex: John Wiley & Sons Ltd; 2010. p. 135. [6] Yoon SB, Cho CW, Cho D, Park JK, Lee JY. Carbon Lett 2008;9:308–15. [7] Seo JM, Cho D, Park WH, Han SO, Hwang TW, Choi CH, et al. J Biobased Mater Bioenergy 2007;1:331–40.